Rapid effect of treatment of psoriatic erythrocytes with the synthetic retinoid acitretin to increase 8-azido cyclic AMP binding to the RI regulatory subunit

Retinoic acid induced suicidal erythrocyte death

Vitamin A and retinoic acid have previously been shown to confer some protection against a severe course of malaria by fostering the phagocytosis of parasitized erythrocytes. Phagocytosis of erythrocytes is stimulated by phosphatidylserine exposure at the cell surface. The present study has thus been performed to explore the effect of retinoic acid and the specific retinoic acid receptor (RAR) agonist 4-(E-2-[5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl]-1-propenyl) benzoic acid (TTNPB) on erythrocyte annexin V binding, which reflects phosphatidylserine exposure at the cell surface. A 24 hours exposure to either, retinoic acid (3 microM) or TTNPB (3 microM), indeed significantly increased annexin binding, an effect paralleled by decrease of forward scatter reflecting cell shrinkage. According to Fluo3 fluorescence, exposure to either, retinoic acid (10 microM, 24 hours) or TTNPB (10 microM, 6 hours), significantly increased cytosolic Ca(2+)-activity, a known trigger of phosphatidylserine exposure. Infection of erythrocytes with Plasmodium falciparum increased phosphatidylserine exposure, an effect increased in the presence of TTNPB. In conclusion, retinoid acid and TTNPB trigger phosphatididylserine exposure and cell shrinkage of erythrocytes, typical features of suicidal erythrocyte death or eryptosis. The eryptosis could participate in the accelerated clearance of parasitized erythrocytes from circulating blood following treatment with retinoids.

A highly decreased binding of cyclic adenosine monophosphate to protein kinase A in erythrocyte membranes is specific for active psoriasis

A cyclic adenosine monophosphate binding abnormality in psoriatic erythrocytes that could be corrected by retinoid treatment has been reported. It was tested whether this binding abnormality is specific for psoriasis and the effects of treatment were compared with etretinate, cyclosporine A, or anthralin on 2-(3)H-8-N(3)-cyclic adenosine monophosphate binding to the regulatory subunit of protein kinase A in erythrocyte membranes. One hundred and fifteen individuals were evaluated, including: (i) 34 healthy persons; (ii) 15 patients with nonatopic inflammatory skin diseases (eczema, erythroderma, tinea, Grover's disease, erysipelas, urticaria); (iii) eight with other dermatoses mediated by immune mechanisms (systemic lupus erythematosus, lichen planus, necrotizing vasculitis, erythema nodosum, systemic sclerosis); (iv) 14 with generalized atopic dermatitis; and (v) 44 with psoriasis vulgaris clinically assessed by Psoriasis Area and Severity Index. In psoriasis, the course of the binding of 2-(3)H-8-N(3)-cyclic adenosine monophosphate to erythrocytes was measured in nine patients during a 10 wk treatment with etretinate, in 21 patients during a 10 wk treatment with cyclosporine A, and one patient under topical treatment with anthralin for 4 wk. We found the following femtomolar binding per mg protein: (i) healthy persons (1064 +/- 124, mean +/- SD); (ii) nonatopic inflammatory skin diseases (995 +/- 103); (iii) immune dermatoses (961 +/- 92); (iv) atopic dermatitis (960 +/- 110); and (v) psoriasis (645 +/- 159; p < 0.0001 compared with nonpsoriatics, Mann-Whitney U test). Treatment of psoriasis with etretinate, cyclosporine A, or anthralin normalized the binding of cyclic adenosine monophosphate, which was inversely correlated to the Psoriasis Area and Severity Index score. It was concluded that the decreased binding of cyclic adenosine monophosphate to protein kinase A in erythrocytes is specific for psoriasis and normalizes after successful treatment.

Effects of [D-Ala1] peptide T-NH2 and HIV envelope glycoprotein gp120 on cyclic AMP dependent protein kinases in normal and psoriatic human fibroblasts

In addition to acquired immunodeficiency syndrome (AIDS), persons infected with human immunodeficiency virus often develop cutaneous manifestations, including severe psoriasis. In previous studies, we have established that psoriatic fibroblasts and erythrocytes obtained from psoriatic patients exhibit decreased levels of cyclic adenosine monophosphate (cAMP) dependent protein kinase (PKA) activity and of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA. Because treatment of patients with peptide T (an octapeptide sequence found in the human immunodeficiency virus envelope glycoprotein gp120) has been observed to result in an improvement in the psoriatic condition, studies were initiated to determine if peptide T and gp120 protein treatment of normal and psoriatic human fibroblasts resulted in any changes in PKA. Exposure of psoriatic fibroblasts to peptide T resulted in a time (4 h to 6 d) and dose [10(-14)-10(-8) M] dependent increase in the levels of 8-azido-[32P]cAMP binding to the RI and RII regulatory subunits of PKA, along with a corresponding increase in PKA activity. Peptide T exhibited a biphasic dose dependent response, with maximal effects on PKA noted at 10(-12)M peptide T. Treatment of normal human fibroblasts with peptide T did not result in any change in PKA levels. Conversely, treatment of normal human fibroblasts for 18 h with gp120 protein [10(-13) M] resulted in a significant decrease in the levels of 8-azido-[32P]cAMP binding to RI and RII and in PKA activity. The presence of peptide T blocked this effect of the gp120 protein. These results indicate that peptide T and gp120 protein may inversely alter the intracellular levels of 8-azido-[32P]cAMP binding to RI and RII, and of PKA activity in susceptible cells. These observed changes in the cyclic AMP-PKA signaling pathway, a biochemical marker for psoriasis, may offer some mechanistic insight into the noted beneficial effects of peptide T treatment, including an improvement in psoriatic lesions.

Oxidative modulation of cyclic AMP-dependent protein kinase in human fibroblasts: possible role in psoriasis

Previous studies have established that cyclic AMP-dependent protein kinase (PKA) activity, as well as 8-azido-[32P]-cAMP binding to the RI and RII regulatory subunits, are decreased in cells from psoriatic patients compared to cells from normal patients. Here we show that the exposure of normal human dermal fibroblasts in culture to hydrogen peroxide and to oxygen free-radical generating systems decreased PKA activity, as well as cyclic AMP binding to the RI and RII regulatory subunits, to levels similar to those observed with psoriatic fibroblasts. Likewise, treatment of normal cytosolic preparations of PKA, as well as purified bovine PKA II, in vitro with free radical generating systems also resulted in decreased PKA activity and 8-azido [32P]-cAMP binding to the RI and RII regulatory subunits. Further, treatment of psoriatic fibroblasts with free radical scavenging agents such as vitamins E and C, and mannitol, and also with superoxide dismutase, restored the ability of RI and RII to bind 8-azido-[32P]-cAMP toward normal levels. Western blot analysis showed that the protein levels of the RI and RII subunits are similar in normal and psoriatic fibroblasts, and that the amounts of RI and RII are not altered by treatment of the cells with free radical-generating systems. These results suggest that oxidative modification may serve as a mechanism to alter PKA activity in human cells, and that an altered oxidative state may be involved in mediating the decrease in PKA activity and cyclic AMP binding noted in cells from psoriatic patients.

Antioxidant enzymes in psoriatic fibroblasts and erythrocytes

Antioxidant enzyme activities in fibroblasts and erythrocytes prepared from normal and psoriatic patients were measured and compared. The most significant differences were noted in superoxide dismutase (SOD) activities. A dramatic (5.2-fold) increase in Mn-SOD activity along with a lesser (1.8-fold) increase in CuZn-SOD activity was observed in fibroblasts from lesional and nonlesional psoriatic skin. The increase of Mn-SOD activity was correlated with an increase of both protein and mRNA. A slight (1.2-fold) increase in CuZn-SOD activity was also found in psoriatic as compared to normal red blood cells, while Mn-SOD activity was not present in these cells. In contrast, both glutathione peroxidase and catalase activities were only slightly (1.3-fold) increased in psoriatic fibroblasts, with no appreciable change noted in psoriatic erythrocytes. Likewise, glutathione levels were observed to be similar in normal and psoriatic cells. The increases in SOD activities did not appear to correlate with the severity of the disease as expressed by the Psoriatic Area Severity Index score or with plasma inflammatory markers. These results demonstrate that antioxidant enzyme activities, particularly Mn-SOD in fibroblasts and CuZn-SOD in erythrocytes, are significantly elevated in cells from psoriatic patients.

Retinoylation of the type II cAMP-binding regulatory subunit of cAMP-dependent protein kinase is increased in psoriatic human fibroblasts

Previously, we have reported a defect in the cAMP-dependent protein kinases (cAMP-PK) in psoriatic cells (i.e., a decrease in 8-azido-[32P]cAMP binding to the regulatory subunits and a decrease in phosphotransferase activity) which is rapidly reversed with retinoic acid (RA) treatment of these cells. This led us to examine a possible direct interaction between retinoids and the RI and RII regulatory subunits through retinoylation. Retinoylation of RI and RII present in normal and psoriatic human fibroblasts was analysed by [3H]RA treatment of these cells, followed either by chromatographic separation of the regulatory subunits or by their specific immunoprecipitation. These studies indicated that RI and RII can be retinoylated. [3H]RA labeling of the RII subunit was significantly (P < 0.005) greater in psoriatic fibroblasts (nine subjects; mean 7.47 relative units +/- 1.37 SEM) compared to normal fibroblasts (eight subjects; mean 2.46 relative +/- 0.49 SEM). [3H]RA labeling of and the increase in 8-azido-[32P]-binding to the RI and RII subunit in psoriatic fibroblasts showed a similar time course. This suggests that the rapid effect of retinoic acid treatment to enhance 8-azido-[32P]-cAMP binding to the RI and RII in psoriatic fibroblasts may be due, in part, to covalent modification of the regulatory subunits by retinoylation.

Post-translational abnormality of the type II cyclic AMP-dependent protein kinase in psoriasis: modulation by retinoic acid

Previously, we have reported a decrease in the binding of a cAMP analog to the regulatory subunits of cAMP-dependent protein kinase (cAMP-PK), as well as a decrease in cAMP-PK activities, in psoriatic cells. Retinoic acid (RA) treatment of these cells can induce an increase in cAMP-PK toward normal levels. To better define the effect of retinoic acid on the cAMP-PK system in psoriatic fibroblasts, Western blot analysis using an RII alpha specific antibody and in vivo phosphorylation experiments were carried out to determine possible changes in the RII regulatory subunit. Our results indicate a decrease in the binding of the cAMP analog 8-azido-[32P]-cAMP with no change in the level of RII protein in psoriatic fibroblasts. In addition, by two-dimensional gel electrophoresis we observed the presence of a phosphorylated form of RII unique to psoriatic cells which is suppressed by RA treatment. This study suggests an altered posttranslational modification of the cAMP-PKII in psoriatic fibroblasts which can be reversed by exposure of these cells to RA.

Fumaric acid derivatives evoke a transient increase in intracellular free calcium concentration and inhibit the proliferation of human keratinocytes

Systemic administration of fumaric acid (FA) derivatives was originally an empirical antipsoriatic treatment, which showed promising clinical results. In the present study, FURA-2-loaded suspensions of cultured normal keratinocytes and SV40-transformed keratinocytes (SVK-14 cells) were used to study the effects of FA derivatives on the intracellular free calcium concentration ([Ca2+]i). Monomethylfumarate (MMF), dimethylfumarate (DMF) and monoethylfumarate (MEF) induced a rapid, transient [Ca2+]i increase in both cell types. This immediate increase reached maximal values of 396 nmol/l 10s after addition of MMF, and fell to basal values within 90-120 s (173 nmol/l for normal keratinocytes and 68 nmol/l for transformed keratinocytes). This increase was not affected by the prior addition of EGTA, indicating that FA derivatives released Ca2+ mainly from intracellular stores into the cytoplasm. Subsequently, dose-dependent inhibitory effects of FA derivatives on keratinocyte proliferation were demonstrated. The results of these experiments revealed that DMF was the most potent, MMF and MEF intermediate, and FA and malonic acid the least potent growth inhibitors. These antiproliferative effects of FA derivatives might be linked to the observed, transient [Ca2+]i elevations.